This application claims the benefit of Korean Application No. 2001-81151, filed Dec. 19, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a transfer efficiency enhancement method and apparatus for use in electronic photograph development equipment, and more particularly, to a transfer efficiency enhancement method and apparatus for use in electronic photograph development equipment in which current trigger and paper sheet recognition are combined with an analog-to-digital converter (ADC) by using a high-impedance transfer roller.
2. Description of the Related Art
In general, electronic photograph development equipment is used in copy machines, laser printers, facsimile machines, etc., in which image data captured from a predetermined script or source is exposed to a photosensitive material to form an electrostatic latent image, a developer is deposited on the position where the electrostatic latent image has been formed, to form a visible image, and the visible image is transferred on a printing paper sheet and then fixed thereon to obtain a desired printed image.
The electronic photograph development equipment, which is used in equipment such as copy machines, laser printers, and facsimile machines, is the most widely used apparatus for printing high-resolution images. Although, the electronic photograph development equipment is still expensive, the electronic photograph development equipment is being widely distributed due to remarkable printing performance in areas such as high-speed printing, excellent printing state, and preservation.
According to the transfer characteristics of the electronic photograph development equipment, an appropriate voltage in the electronic photograph development equipment should be applied to a transfer roller so that an image may be transferred in an optimal state. Accordingly, a bad transfer does not occur. In the case that the transfer voltage is low (lower than the optimal state), an electrostatic force is weak and thus toner does not efficiently stick on a sheet of paper. Accordingly, a tremble occurs at the time of transferring. Further, in the case that the transfer voltage is high (higher than the optimal state), the toner on a photosensitive drum is counter-charged with a result that the toner does not stick on the sheet of paper, or an electrostatic force generated from the transfer roller is strong with a result that a toner is transferred on a sheet of printing paper before the printing paper approaches the photosensitive drum, thereby causing the image to be scattered. Thus, only if an appropriate transfer voltage is applied on the sheet of printing paper can a bad transfer be prevented and accordingly a transfer efficiency be enhanced.
Thus, the electronic photograph development equipment is provided with a transfer voltage recognition device which converts a load current flowing through a load of a transfer roller into a voltage, and adjusts a transfer voltage according to a voltage detected by applying a constant voltage of a predetermined level to the conversion voltage, which is obtained by converting the load current flowing through the load of the transfer roller into a voltage.
According to a general transfer environment recognition method, a current flowing through a load is feedback, the fedback current is converted into a voltage, and then the conversion voltage is read. Accordingly, a resistance value of the transfer load is recognized. Then, a final transfer voltage is determined with the resistance value of the recognized transfer load. Thus, a drawback of the contact-type transfer roller sensitive to variation of the transfer environment has been complemented so that a transfer efficiency is optimized.
Basically, two methods exist for sensing (or recognizing) a transfer voltage (or transfer current) and controlling the sensed voltage (or current). The first method is a current trigger method illustrated in FIG. 1, in which a transfer voltage is determined by detecting a voltage which causes a predetermined current to flow through the transfer roller. In this method, a voltage which causes a predetermined current to flow through the transfer roller is detected and then a transfer voltage is determined according to a previously prepared transfer voltage table illustrated in the following Table 1.
FIG. 1 shows a transfer timing diagram of a current trigger transfer method, which implements a section obtaining a transfer voltage by increasing a voltage at an initial time until a predetermined current flows through a transfer roller, and another section transferring the determined transfer voltage on a sheet of paper.
The current trigger method has a problem that the transfer efficiency can vary by each sheet of paper because the transfer voltage is determined irrespective of the kind of the sheet of paper. Also, although the resistance of the transfer roller should be high in order to reduce paper sheet deviation, a high-impedance transfer roller may not be triggered in the case of a low-temperature, low-humidity environment.
The second method is a transfer method, which considers a paper sheet resistance as shown in FIG. 2, in which a fixed voltage is applied to a transfer roller to measure a resistance Rtr+Ropc between the transfer roller and developer, and another fixed voltage is applied to a section of a sheet of paper about several millimeters from a leading end of the sheet of paper immediately after the sheet of paper has been advanced in the same manner to measure a system resistance Rtr+Rpaper+Ropc between the transfer roller and the developer, to thereby determine a final transfer voltage. Rtr denotes a resistance of the transfer roller, Ropc denotes a resistance of the developer (OPC), and Rpaper denotes a resistance of the sheet of paper.
FIG. 2 shows a transfer timing diagram of the transfer method considering the resistance of a sheet of paper, which implements a transfer environment recognition section recognizing a resistance between a transfer roller and a developer at an initial time, a subsequent paper sheet recognition section recognizing a resistance of a sheet of paper, and a final section transferring a transfer voltage determined by using a system resistance to the sheet of paper.
The paper sheet recognition transfer method has the following problems. Since a trigger is triggered by only a fixed voltage when a system resistance is recognized only with a transfer roller and a developer before a sheet of paper has been advanced, an area where a trigger can be triggered is narrow. Also, since a deviation in resistance can be large according to a device peripheral environment, determining a fixed voltage can be difficult. Further, since an area where a trigger can be triggered varies according to a magnitude of the applied voltage in view of the circuitry features, determining a voltage at which a trigger can be triggered under all environments can be difficult.
Also, since the system resistance is small, a band may be generated at a halftone in case of a high set voltage under a high-temperature and high-humidity environment, and a positive (+) cleaning effect may be insignificant in case of a low set voltage under a low-temperature and low-humidity environment. Since a transfer voltage is determined by using a resistance recognized immediately after a sheet of paper has been advanced, the resistance of the paper sheet is not accurately recognized in the case that a skew of the paper sheet has occurred. As a result, a transfer efficiency may be sharply lowered. To prevent this phenomenon, the resistance of the transfer roller is made higher than that of the sheet of paper. However, in the case where a high-impedance transfer roller is used, a non-trigger phenomenon may occur under a low-temperature and low-humidity environment.
For this purpose, a transfer voltage controlling technology has been used. According to a conventional transfer voltage controlling method, a predetermined transfer voltage is output from a transfer voltage generator through a pulse-width modulation (PWM) control, and thus a transfer current is sent to a transfer load. The current value is converted into a voltage through a detection resistor. Then, a reference voltage is established so that a comparator is triggered when a current not lower than a preset reference current value flows. Accordingly, a transfer load value is recognized when the comparator is triggered. However, this method should indicate a point in time when the comparator is triggered by sequentially increasing the voltage output from the transfer voltage generator from a lower voltage to a higher voltage through an electronic control PWM increase. As a result, since the range of the transfer resistance is usually wide, to perform a step-up operation can take considerable time. In particular, in this case, if a system runs at high speed, an operational fault may occur. Since a transfer current is fixed as a set current value, and thus the voltage output from the transfer voltage generator is controlled until reaching the reference voltage of the comparator, a deviation due to a load range is very small based on the transfer load operating in proportion with the output voltage irrespective of the range of the transfer load.
As an alternative method, the voltage output from the transfer voltage generator is fixed, and then a feedback current value is detected. Then, the detected current value is converted into a voltage, and the conversion voltage is converted from an analog signal to a digital signal to be read to identify a transfer load. This method will be described in more detail with reference to FIGS. 3A and 3B.
FIG. 3A is a circuit diagram showing a general transfer voltage recognition apparatus. As shown in FIG. 3A, to recognize an actual transfer voltage output from a transfer voltage generator 10, a high-level transfer voltage VTHV from the transfer voltage generator 10 is applied to a load resistor RL that is a transfer load. A voltage detection resistor R1, has one end connected to the transfer voltage generator 10, inserted along a closed circuit path formed by the transfer voltage generator 10 and the load resistor RL, and a variable resistor VR, whose one end is connected to the other end of the voltage detection resistor R1 and has the other end commonly grounded together with the load resistor RL, in order to detect a transfer current IL incoming to the load resistor RL as a voltage form. Here, the magnitude of the transfer current IL applied to the voltage detection resistor R1 can be adjusted with the variable resistor VR so that a level of the voltage VS (hereinafter called an S-node voltage) detected at a node S which is a common node between the transfer voltage generator 10 and the voltage detection resistor R1 can be adjusted. Also, a constant voltage end VCC is connected to a common node between the variable resistor VR and the voltage detection resistor R1 so that a constant voltage of a predetermined level is applied to a common node between the variable resistor VR and the voltage detection resistor R1 to produce the S-node voltage of the voltage detection resistor R1. Meanwhile, if the S-node voltage detected through the voltage detection resistor R1 is applied to a second operational amplifier OP2 via resistors Ra and Rb, the second operational amplifier OP2 performs an integration and amplification function via a feedback resistor RC and a feedback capacitor C1, with the S-node voltage, so that the S-node voltage is altered into a direct-current voltage of approximately 0-5 V which can be recognized in an analog-to-digital converter (ADC) 20. The analog-to-digital converter (ADC) 20 performs a function of converting the analog voltage output from the operational amplifier OP2 into a digital value. Also, a transfer voltage controller 30 receives the digital value output from the analog-to-digital converter (ADC) 20, and compares the input digital value that is a transfer voltage with a preset reference transfer voltage. Then, if the input digital value and the preset reference transfer voltage differ, the transfer voltage controller 30 applies a pulse-width modulation command corresponding to the difference between the input digital value and the preset reference transfer voltage to a pulse-width modulator 40. Then, when the pulse-width modulator 40 having received the pulse-width modulation command outputs a pulse-width modulation value corresponding to the pulse-width command, a first operation amplifier OP1 amplifies the pulse-width modulation value and applies an amplified result to the transfer voltage generator 10, so that a stable transfer voltage can be supplied. For example, the transfer voltage controller 30 is configured to include a central processing unit 31 correcting a difference between the supplied transfer current and the current detected in the actual load resistor through a pulse-width modulation (PWM) process, and a memory 32 storing a reference transfer voltage digital value and simultaneously storing pulse-width modulation values based on the digital values detected via the analog-to-digital converter (ADC) 20 and the reference transfer voltage digital value in the form of a lookup table (LUT). Although this method is appropriate for a speedy system since the method does not require more time for step-up and triggering than the above-described first method, the transfer efficiency is difficult to distinguish because the difference between the analog-to-digital conversion values and the reference transfer voltage digital value is gradually reduced as the transfer load becomes large, and the difference under a high-impedance environment is also difficult to recognize.
Meanwhile, a transfer control method in electronic photograph development equipment adopting a contact-type roller method has a sensitivity to both of a transfer roller according to a transfer environment and a variation of a transfer condition according to the thickness of a sheet of paper. Accordingly, an environment recognition method controlling the sensitivity of a transfer roller and the variation of a transfer condition is regarded as being important. Thus, a resistance value with respect to the transfer roller is basically read in correspondence to the fluctuation. As a result, the environment is recognized to perform a transfer voltage control. For example, in order to correct an error with respect to sheet thickness of a sheet of paper, typically, the resistance value is read to perform a transfer voltage control appropriate for the resistance value, which is read, when the sheet of paper has advanced between a photosensitive drum and the transfer roller. However, the conventional method has the following drawback in recognizing the thickness of the sheet of paper. That is, when the sheet of paper has advanced between the photosensitive drum and the transfer roller, the conventional method recognizes only the resistance of the advanced sheet of paper irrespective of a size of the sheet of paper. Accordingly, sheets of paper having the same thickness but different size may be recognized as sheets of paper each having a different thickness, which impedes a finite high-voltage control.
To solve the above problems, an electronic photograph development device which improves a recognition degree of a transfer environment is provided, as shown in FIG. 3B. The range of the transfer load is recognized and then a pulse-width modulation output is stepwise applied within the recognized range of the transfer load, to thereby recognize the transfer load. Thus, transfer load recognition at high speed and accuracy is attempted, and the precision of the paper sheet thickness recognition is enhanced through a proportional correction based on the size of an inserted sheet of paper.
As shown in FIG. 3B, a transfer environment recognition apparatus recognizes a transfer environment in existing electronic photograph development equipment. In FIG. 3B, a pulse-width modulator 110 receives a pulse-width modulation command and outputs a pulse-width modulation value. A transfer voltage generator 120 applies a transfer voltage corresponding to the pulse-width modulation value to a transfer load RL. A feedback voltage detector 130 receives a transfer current IL output from the transfer voltage generator 120 and flowing through the transfer load RL and converts the fedback transfer current into a voltage via a detection resistor RS1, to thereby detect a feedback transfer voltage. A feedback voltage smoothing amplifier 140 smoothes the fedback transfer voltage and amplifies the fedback transfer voltage at a predetermined amplification factor. An analog-to-digital converter 150 converts the analog output from the feedback voltage smoothing amplifier 140 into a digital signal. A trigger point-in-time detector 160 compares a predetermined trigger reference voltage with the output from the feedback voltage smoothing amplifier 140 and detects a point-in-time when the output from the feedback voltage smoothing amplifier 140 becomes larger than the trigger reference voltage as a trigger point-in-time. A paper sheet size recognizer 170 recognizes a size of an advanced sheet of paper. A lookup table (LUT) 180 stores a transfer voltage corresponding to respective transfer loads RL and the thickness of the sheets of paper as a lookup table. A microcomputer 100 determines a transfer voltage. The microcomputer 100 reads the output from the analog-to-digital converter (ADC) 150 with the output voltage of the transfer voltage generator 120 fixed, and thus calculates an approximate range of the transfer load RL. Then, the microcomputer 100 controls the output voltage of the transfer voltage generator 120 so as to increase stepwise from the lowest value of the approximate range of the transfer load RL, and detects the trigger point-in-time via the trigger point-in-time detector 160. Then, the microcomputer 100 calculates an accurate transfer load RL using a relationship between the output voltage of the transfer voltage generator 120 and the set trigger current, and calculates the thickness of the paper sheet through a proportional correction according to a ratio of the size of the sheet of paper provided from the paper sheet recognizer 170. Then, the microcomputer 100 determines the transfer voltage corresponding to the calculated transfer load and the thickness of the sheet of paper from the lookup table LUT 180.
Here, the microcomputer 100 measures a no-paper transfer resistance value which is a resistance value between the transfer roller and the photosensitive drum at a state where no paper sheet has advanced, and calculates a non-standard paper sheet transfer resistance value which is a resistance value between the transfer roller and the photosensitive drum at a time when a non-standard paper sheet has advanced. Then, the microcomputer 100 calculates the thickness of a sheet of paper, by using a transfer resistance value obtained by converting the non-standard paper sheet transfer resistance value into a value obtained when a standard sheet of paper of a same thickness has advanced.
In the transfer environment recognition apparatus for use in the electronic photograph development equipment, if a printing signal is input, a light exposure device is driven, a fixing device is heated, and a main motor is driven, to thereby perform a warming-up to print and to subsequently pick-up a sheet of paper. In this case, since a transfer environment should be recognized, a reference transfer voltage is output in order to identify a transfer load RL. Then, the size of a sheet of paper, which is being fed is recognized through a paper sheet size recognizer 170, and provided to a microcomputer 100. The microcomputer 100 having received the recognized paper sheet size information calculates the thickness of the paper sheet accurately through a proportional correction according to the size of the sheet of paper, and then performs a finite high-voltage transfer control for each sheet of paper. However, since an optimal transfer voltage is not calculated depending upon the change of the transfer environment and the result of the paper sheet recognition, a transfer efficiency is lowered.
Meanwhile, a laser beam printer is divided into a cleaner-less system and a cleanable system according to presence or absence of a cleaning member such as a cleaning blade and a cleaning roller. Both the systems require a higher transfer efficiency than a certain degree. Cleanable systems affect the volume of a used toner vessel and a lifetime of a developer directly, while a cleaner-less system causes deterioration of an image, as ghost images are generated.
An object of the present invention is to provide a transfer efficiency enhancement method and apparatus for use in electronic photograph development equipment which determines a transfer voltage positively according to a transfer environment and a sheet of paper, to thereby obtain a higher transfer efficiency than a predetermined level.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Another object of the present invention is to provide a transfer efficiency enhancement method and apparatus for use in electronic photograph development equipment having a higher transfer efficiency than a predetermined level, in which a system resistance is read by increasing a transfer voltage by a predetermined value with only a value from an analog-to-digital converter at the time of recognizing a transfer environment, and a resistance of a sheet of paper is read by using a circuit which has been used to recognize the transfer environment without focusing on calculation of the thickness of the sheet of paper at the time of recognizing the sheet of paper, to thus apply the voltage value applied to the leading end of the actual paper sheet as a transfer voltage value of the whole sheet of paper.
An additional object of the present invention is to provide a transfer efficiency enhancement method and apparatus for use in electronic photograph development equipment having a higher transfer efficiency than a predetermined level, in which a predetermined voltage is added to or from a voltage applied to the leading end of a sheet of paper by considering a resistance value of a system including the sheet of paper, in proportion with a system resistance, to thereby determine an optimal transfer voltage, in which a high-impedance transfer roller is used to obtain a higher transfer efficiency than a predetermined level even though the system resistance has been recognized as too low before the sheet of paper is fed because of slippage of the sheet of paper.
To accomplish the above and other objects, a transfer efficiency enhancement method for enhancing a transfer efficiency by controlling a transfer voltage output from a transfer voltage generator through a pulse-width modulation command under the control of a microcomputer according to a transfer environment and a paper sheet recognition in electronic photograph development equipment is provided. The transfer efficiency enhancement method comprises: recognizing a current transfer environment by increasing a transfer voltage up to a predetermined value until a trigger is triggered before a sheet of paper is fed, according to an analog-to-digital conversion value of a fedback transfer voltage; recognizing the sheet of paper by applying a transfer voltage determined by recognition of the transfer environment to a leading end of the sheet of paper, in order to perform recognition and transfer of the sheet of paper; and controlling the transfer voltage based on an output value from an analog-to-digital converter (ADC) which is obtained in a result of the paper sheet recognition, in which the transfer voltage is controlled to become high if the ADC output value is large, but the transfer voltage is controlled to become low if the ADC output value is small.
The transfer environment recognition may comprise: tabulating the analog-to-digital conversion value of the fedback transfer voltage which is determined in correspondence to the system resistance and the transfer voltage, in a lookup table; measuring the analog-to-digital conversion values of an actual transfer voltage and the fedback transfer voltage; and finding out the system resistance from the lookup table according to the measured analog-to-digital conversion value, and outputting the system resistance.
Further, the paper sheet recognition may comprise finding out the transfer voltage determined by the system resistance including the recognized resistance of the sheet of paper from the lookup table.
The transfer voltage controlling may comprise adding or subtracting a predetermined voltage with respect to the voltage applied to the leading end of the sheet of paper in proportion with the system resistance according to the analog-to-digital conversion value of the fedback transfer voltage, to thereby determine an optimal transfer voltage.
Also provided is a transfer efficiency enhancement apparatus enhancing a transfer efficiency by controlling a transfer voltage according to a transfer environment and a paper sheet recognition in electronic photograph development equipment, the transfer efficiency enhancement apparatus comprising: a high-impedance transfer roller; a paper sheet resistance recognizer recognizing a resistance of the sheet of paper; a lookup table in which optimal transfer voltages are tabulated according to a system resistance including the resistance of the sheet of paper of the paper sheet resistance recognizer; a transfer voltage generator generating an optimal transfer voltage for the high-impedance transfer roller; an analog-to-digital converter analog-to-digital converting the transfer voltage fedback from the transfer voltage generator and outputting the analog-to-digital conversion value; a trigger point-in-time detector comparing the fedback transfer voltage with a trigger reference voltage and detecting a trigger point-in-time; a microcomputer recognizing a current transfer environment by increasing a transfer voltage up to a predetermined value until a trigger is triggered before a sheet of paper is fed, recognizing a sheet of paper by applying a transfer voltage determined by recognition of the transfer environment to the leading end of the sheet of paper, in order to perform recognition and transfer of the sheet of paper, and referring to the lookup table to find out the optimal transfer voltage, and controlling the optimal transfer voltage from the transfer voltage generator to the high-impedance transfer roller, in which the transfer voltage is controlled to become high if the ADC output value is large, but the transfer voltage is controlled to become low if the ADC output value is small, based on the output value from an analog-to-digital converter (ADC) which is obtained in the result of the paper sheet recognition, and a switching unit connected to the output end of the transfer voltage generator, transferring the transfer voltage to the paper sheet recognizer by a trigger signal from the trigger point-in-time detector.